Effects of solar wind parameters on the development of magnetospheric substorms     

Takashi Murayama  Kazuyuki Hakamada 《Planetary and Space Science》1975,23(1):75-91

Effects of solar wind parameters on the development of substorms during the events of southward interplanetary magnetic field (IMF) lasting more than one hour were studied. Analysis on 175 events with average magnitude of the southward component of IMF larger than l·5γ as observed in July–December 1965 lead to the following results: (1) The total auroral electrojet (AEJ) current associated with the southward IMF event is approximately proportional to the time integral of the magnitude of the southward component. (2) The azimuthal component of IMF also affects the AEJ development. AEJ about twice as intense were observed when IMF was directed duskward than when IMF was directed dawnward. (3) AEJ intensity is strongly affected by the solar wind velocity during the southward IMF events, the intensity being approximately proportional to the square of the velocity. (4) No indication was found that the angle between the Sun-Earth line and the Earth's dipole axis plays any role on the development of substorms if effects of the solar wind parameters as described above are eliminated.  相似文献   

Spectroscopic Studies of Solar Corona VII. Formation of a Coronal Loop by Evaporation     

Jagdev?SinghEmail author  Takashi?Sakurai  Kiyoshi?Ichimoto  Isao?Suzuki  Masaoki?Hagino 《Solar physics》2005,226(2):201-221

We obtained time-sequence spectroscopic observations in (Fe x) 6374 Å and (Fe xiv) 5303 Å lines successively with the 25-cm coronagraph, and narrow-band and Doppler images in 5303 Å line by the 2-D 10-cm Doppler coronagraph NOGIS at the Norikura Solar Observatory, of a coronal region for about 7 h on 9 19–20, 2001. The raster scans were obtained with a quasi-periodicity of about 14 min and NOGIS obtained the images with an interval of about 1 min. The coronal region observed showed the formation of a coronal loop by a high-speed surge in the 6374 Å line rising from one of the footpoints of the loop. Off the limb spectroscopic observations in the 6374 Å line showed large velocities along the line of sight and vertical to the solar limb at the time of formation of the loop. The 5303 Å line observations showed negligible line-of-sight velocities and low vertical velocities when compared to those in the 6374 Å line. A hump in the intensity plots in 5303 Å with height appears to move up with respect to the solar limb with an average velocity of 4km s^–1. The FWHM of the 6374 Å showed a much smaller value of about 0.7 Å near the foot point as compared to a value of 1.2 Å at larger heights at the beginning of observations. Later as the loop developed, the FWHM of 6374 Å line showed a gradual decrease along the loop up to 70 from the limb, reached a minimum value of about 0.5 Å and then increased with height during the formation of the loop; this trend lasted for about 2 h. About 3 h after the beginning of the formation of the loop, the FWHM of 6374 Å emission line showed normal values and normal rate of increase with height with some fluctuations. The FWHM of the 5303 Å line did not show such variations along the loop and showed normal decrease in FWHM with height found earlier (Singh et al., 2003a). These observations suggest that a relatively cooler plasma at a temperature of about 0.7 MK or less (corresponding to minimum value of FWHM of 0.5 Å) was ejected from the transition region with a large velocity of about 48km s^–1, heated up in the corona by some process and formed a coronal loop with a height of about 200 above the limb that had lifetime greater than 4 h. It appears that the plasma moved from one of the footpoints and the loop was formed by evaporation of chromospheric plasma. No large-scale brightening and H flare were observed in this region during the observational period of 7 h.On leave from Indian Institute of Astrophysics, Bangalore 560034, India.  相似文献   

Dynamical rupture process on a three-dimensional fault with non-uniform frictions and near-field seismic waves   总被引：1，自引：0，他引：1  

Takeshi Mikumo  Takashi Miyatake 《Geophysical Journal International》1978,54(2):417-438

Summary. Dynamical rupture process on the fault is investigated in a quasi-three-dimensional faulting model with non-uniform distributions of static frictions or the fracture strength under a finite shearing pre-stress. The displacement and stress time functions on the fault are obtained by solving numerically the equations of motion with a finite stress—fracture criterion, using the finite difference method.
If static frictions are homogeneous or weakly non-uniform, the rupture propagates nearly elliptically with a velocity close to that of P waves along the direction of pre-stress and with a nearly S wave velocity in the direction perpendicular to it. The rise time of the source function and the final displacements are larger around the centre of the fault. In the case when the static frictions are heavily non-uniform and depend on the location, the rupture propagation becomes quite irregular with appreciably decreased velocities, indicating remarkable stick-slip phenomena. In some cases, there remain unruptured regions where fault slip does not take place, and high stresses remain concentrated up to the final stage. These regions could be the source of aftershocks at a next stage.
The stick—slip faulting and irregular rupture propagation radiate high-frequency seismic waves, and the near-field spectral amplitudes tend to show an inversely linear frequency dependence over high frequencies for heavily non-uniform frictional faults.  相似文献   

Far-infrared properties of metallic dust grains     

Toshihiko Tanabé  Takashi Onaka  Fumio Kamijo 《Astrophysics and Space Science》1984,98(2):323-342

Far-infrared properties of metallic particle are reinvestigated in detail. In the far-infrared region, absorption due to the eddy current generally dominates over that obtained by using the Rayleigh approximation erroneusly. The wavelength dependence of the eddy current term is examined carefully and shown to be less steep than that predicted by the Rayleigh approximation for dust grains larger than 100 nm in radius. It also depends more sensitively on the grain size. A wider temperature distribution is expected corresponding to a given size distribution and hence the emission spectrum becomes less steep than the preductions by the Rayleigh approximation. Iron and graphite particles are investigated as typical interstellar metallic grains. Effects of coating of dielectric materials are also examined. Comparisons with experimental results and with observations are discussed.  相似文献   

Preliminary observation of missing energy flux of sunspot     

Tadashi Hirayama  Tomizo Okamoto 《Solar physics》1981,73(1):37-43

We have searched for the missing energy flux of the sunspot by measuring white-light photographs over the region around the sunspots exceeding ten times of the diameter of spots. It was found that the excess brightness amounts to 0.3–0.8% of the local continuum intensity immediately beyond the penumbra and smoothly decrease to zero at the edge of our inspected radii of 130 000–160000km. This result suggests that the flux deficit in sunspots of the order of 30% over the umbra-penumbra is roughly the same as the excess flux found in the very large surrounding region which includes photospheric facular contributions. Among nineteen spots fourteen showed this extended bright ring. Narrow band photoelectric scans revealed that the excess radiation originates in the continuum, not from weakened absorption lines.  相似文献   

Arsenic accumulation and distribution in tissues of black-footed albatrosses     

Fujihara J  Kunito T  Kubota R  Tanaka H  Tanabe S 《Marine pollution bulletin》2004,48(11-12):1153-1160

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Concentration and subcellular distribution of trace elements in liver of small cetaceans incidentally caught along the Brazilian coast     

Kunito T  Nakamura S  Ikemoto T  Anan Y  Kubota R  Tanabe S  Rosas FC  Fillmann G  Readman JW 《Marine pollution bulletin》2004,49(7-8):574-587

Concentrations of trace elements (V, Cr, Mn, Fe, Co, Cu, Zn, Ga, As, Se, Rb, Sr, Mo, Ag, Cd, Sb, Cs, Ba, T-Hg, Org-Hg, Tl and Pb) were determined in liver samples of estuarine dolphin (Sotalia guianensis; n = 20), Franciscana dolphin (Pontoporia blainvillei; n = 23), Atlantic spotted dolphin (Stenella frontalis; n = 2), common dolphin (Delphinus capensis; n = 1) and striped dolphin (Stenella coeruleoalba; n = 1) incidentally caught along the coast of Sao Paulo State and Parana State, Brazil, from 1997 to 1999. The hepatic concentrations of trace elements in the Brazilian cetaceans were comparable to the data available in literature on marine mammals from Northern Hemisphere. Concentrations of V, Se, Mo, Cd, T-Hg and Org-Hg increased with increasing age in liver of both estuarine and Franciscana dolphins. Very high concentrations of Cu (range, 262-1970 microg/g dry wt.) and Zn (range, 242-369 microg/g dry wt.) were observed in liver of sucklings of estuarine dolphin. Hepatic concentrations of V, Se, T-Hg, Org-Hg and Pb were significantly higher in estuarine dolphin, whereas Franciscana dolphin showed higher concentrations of Mn, Co, As and Rb. Ratio of Org-Hg to T-Hg in liver was significantly higher in Franciscana dolphin than estuarine dolphin, suggesting that demethylation ability of methyl Hg might be lower in liver of Franciscana than estuarine dolphins. High hepatic concentrations of Ag were found in some specimens of Franciscana dolphin (maximum, 20 microg/g dry wt.), and 17% of Franciscana showed higher concentrations of Ag than Hg. These samples with high Ag concentration also exhibited elevated hepatic Se concentration, implying that Ag might be detoxified by Se in the liver. Higher correlation coefficient between (Hg+0.5 Ag) and Se than between Hg and Se and the large distribution of Ag in non-soluble fraction in nuclear and mitochondrial fraction of the liver also suggests that Ag might be detoxified by Se via formation of Ag2Se in the liver of Franciscana dolphin.  相似文献   

Microbial responses using denaturing gradient gel electrophoresis to oil and chemical dispersant in enclosed ecosystems     

Yoshida A  Nomura H  Toyoda K  Nishino T  Seo Y  Yamada M  Nishimura M  Wada M  Okamoto K  Shibata A  Takada H  Kogure K  Ohwada K 《Marine pollution bulletin》2006,52(1):89-95

Microbial responses to the addition of oil with or without a chemical dispersant were examined in mesocosm and microcosm experiments by using denaturing gradient gel electrophoresis of bacterial ribosomal DNA and direct cell counting. When a water-soluble fraction of oil was added to seawater, increases in cell density were observed in the first 24h, followed by a decrease in abundance and a change in bacterial species composition. After addition of an oil-dispersant mixture, increases in cell density and changes in community structure coincided, and the amount of bacteria remained high. These phenomena also occurred in response to addition of only dispersant. Our results suggest that the chemical dispersant may be used as a nutrient source by some bacterial groups and may directly or indirectly prevent the growth of other bacterial groups.  相似文献   

Spin rates of fast-rotating asteroids and fragments in impact disruption     

Toshihiko Kadono  Masahiko Arakawa  Takashi Ito  Keiji Ohtsuki 《Icarus》2009,200(2):694-697

We present a new experimental result of fragment spin-rate in impact disruption, using a thin glass plate. A cylindrical projectile impacts on a side (edge) of the plate. Dispersed fragments are observed using a high-speed camera and the spin rates of fragments are measured. We find that the measured fragment spin-rate decreases with increasing size. Assuming that the rotational energy of fragments is supplied from the residual stress, the spin rate ω decreases with increasing fragment size r as ω∼r−1, which explains the above experimental results. This size-dependence is similar to that of the observed spin rates of small fast-rotating asteroids. Our results suggest that spin rates of fragments of small asteroids immediately after disruption may have a similar size-dependence, and can provide constraints on the subsequent spin-state evolution of small asteroids due to thermal torques.  相似文献   

Editorial Appreciation     

John Leibacher  Takashi Sakurai  Lidia van Driel-Gesztelyi 《Solar physics》2009,255(1):1-2

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